It is a cross-sectional study, comparing the prevalence of Helicobacter pylori infection (prevalence of IgG antibodies to H. pylori) in the healthy population of Ubrique and Grazalema (mountain location, mortality from stomach cancer 20/100,000) and in Barbate, (coastal location, mortality from stomach cancer 10/100,000) in the province of Cadiz, southern Spain. The subjects were randomly selected, 163 men and 169 women, 18 years or older; 179 persons were studied in the inland, and 154 in the littoral in January 1997. Of the 332 subjects investigated, 43% were positive, a mean antibody titer of 337 IU/1 (95 % CI: 254-420), and 56% were negative, with a mean titer of 18 IU/1 (95% CI: 15-19). In the coastal population, 30% has positive titers and 54% in the mountain location. By age: 18-40 years, 30% of littoral and 41% of inland population had positive titers; 41-60 years, 35% of those living in the littoral and 58% of inland population had positive titers; > 60 years, 24% of coastal inhabitants and 62% of those living in the inland had positive titers. Living in mountain locations in the province of Cadiz involves a greater ecological risk for H. pylori infection (p < 0.05).